The aim of the study was to analyze the effect of a plant feed additive based on Artemisia absinthium and the metal trace element CoCl₂ (cobalt chloride II) on the metabolism of amino acids closely related to the energy of feed and the bacterial community of the rumen of Kazakh white-headed bulls. Animals were divided into four groups: (A)—the control group of animals received the basic diet (BD), (B)—animals of the experimental group I were additionally given A. absinthium at a dose of 2.0 g/kg of dry matter (DM), (C)—II experimental group A. absinthium at a dose of 2.0 g/kg DM with additional CoCl₂ (1.5 mg/kg/DM), and (D)—III experimental group was given only CoCl₂ (1.5 mg/kg/DM) to study the rumen metabolism of amino acids and bacterial diversity of animals, rumen cannula were installed, the experiment was carried out using a 4 × 4 Latin square. It was found that additional feeding of A. absinthium, both separately and in combination with CoCl₂, led to a change in the indices of the alpha biodiversity of the bacterial community. Correlation analysis revealed a linear relationship between the concentration of amino acids and the rumen bacterial community (p ≤ 0.05). The relationship between the values of amino acid concentrations and certain OTUs was established, with a possible percentile probability of 95% for the genera unclassified Lachnospiraceae, unclassified Clostridiales, unclassified Bacteroidales, Fibrobacter, Ihubacter, Phocaeicola, Paludibacter, Akkermansia, Vampirovibrio, unclassified Ruminococcaceae, and Alistipes. Thus, the use of A. absinthium and CoCl₂ as feed additives, both in combination and without, leads to a change in the taxonomic structure affecting the concentration of amino acids. However, further research is needed to better understand the effectiveness and safety of these supplements.